[AZ-Observing] Meteoric observations need accurate reporting

  • From: "Bill Peters" <afls@xxxxxxx>
  • To: <az-observing@xxxxxxxxxxxxx>
  • Date: Mon, 10 Jun 2002 01:26:07 -0700

To anyone observing a extremely bright bolide (aka:  fireball).

Most of the reportings of the June 9, 2002 fireball are too vague to be able
to triangulate the trajectory and locate a possible fall zone.

There is great scientific value in the recovery of observed falls.  This
best way for recovery of an observed fall that does not land at your feet is
for compilation of accurate reporting by multiple observers.  Even if the
meteor has little chance of recovery or did not even survive entry it is
still possible to compute a rudimentary orbit from accurately reported
sightings and contribute to our understanding of bolides.  Scientists are
theorizing that some Earth crossing meteorites travel in similar orbit
families, but it has not yet been confirmed.  Of significant interest are
the early June bolides and recovered meteorites. Early June holds the
distinction of having both the most observed and recovered fireballs or
anytime during the entire year.  Although there is no indication that this
June 9 bollide landed it still is useful to learn from this event.

Several pointers in reporting your observations of very bright meteors:  no
observer can judge distance nor size of the event, only direction from an
observers location.   Therefore give accurate location of observing site and
precise directional information of the travel path of the bolide.  There are
three primary observable events in the final flight of a bolide; its entry,
its oblation (explosive disintegration, the big flash sometimes multiple),
and its point of dark body state where visibility ends.  It is important to
obtain info on where in the sky the meteor BEGAN, where is oblated
(exploded), and where it ended (reached dark body state).  Most observers
only view the final one or two events.  Essentially all meteorite falls
reach dark body state before hitting the ground.

Once a target area is located from distant observers it is very important to
find the closest observers to the fall site.  I am not surprised none of the
observers reported any sounds.  Likely they were too far away, or else
distracted by what they had seen and their excitement in talking about it.

Sounds are very important to listen for.  Bollide sounds can travel over 50
miles, but the long distance and time delay are not realized by possible
observer/listeners who are not paying attention or do not associate the
sounds with the observed event.  Even the June 7, 1998 Stanfield, AZ Fall
Meteorite people, who were just 8 miles away were surprised, by the sounds
heard 40 seconds later - much later than what one would hear from thunder -
typically heard no more than 20-25 seconds after the strike.  There are two
distinct phenomena on bolide sounds: the simultaneous often radio-like
static created in the same way, and the sonic booms of the meteor in flight.
The sonic booms are the key to judging distances.  The way to time and
listen for them is begin counting immediately after you've seen the flash
(explosion) until you can look at your watch to continue the count.  Cupping
your ears with your hands will greatly enhance your listening ability.  You
will need to keep listening for over 4 minutes.  Sound travels 1 mile per 5
seconds.  Therefore if you do hear and time sounds you can easily compute
distance.  I myself have heard a sonic boom from a military jet on a known
path 45 miles away nearly four minutes after the event.

Here are some basic questions to report after observing a bolide:
1    Where were you when you first saw the meteor?  (Give observing site,
address,or unique identifying info)
2    At what point in the flight did you first notice it?
3    What did you see?
4    Where did it begin -if observed?
    (Give degrees above the horizon, observed beginning point directional
location, background star fields trees, houses, mountains or other markers,
precise direction of travel, repeat for next two questions.  Example: it
began 30* above the horizon at the 1 o'clock position from North just to the
right of the tail star in the Big Dipper traveling ESE, it exploded at 70*
above the horizon at the 10:30 position and I followed it until it reached
the 8 oclock position 20 degrees above the horizon.  It the backgound I
could see its endpoint was just to the right and above the right secondary
peak of the Table Top Mountian.)

5    If is exploded, at what point(s) in the trajectory?
6    Where did it end?
7    Did you hear anything?  What did you hear?
8    Were you able to time how long after seeing the event before hearing
it?
9    How bright was it?  Did you see your shadow?
10  What color was it?  Was the color consistant or did it change?
11  Could you observe a remnant trail after the event?  Where did the trail
end?
12  Who else do you know saw it?  Can they be contacted?

Good reporting from multiple observers from different locations should lead
to plotting a rudimentary orbit and determining a scatter ellipse of a
possible fall search.

Bill Peters 480-813-4242



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